refraction and caustics in cycles
I'm just posting this so I can post the pics - if it ends up being no good, i'll delete this answer. Here are a just a couple of things you can try.
Firstly, make sure both Reflective and Refractive Caustics are enabled in the Render Properties tab:

Also, in Material Properties (for each material used), make sure &quot;Multiple importance&quot; is selected, and &quot;Homogeneous&quot; is disabled.

Lastly, if you're using a denoiser, try turning it down by about half and see if that's what's causing it.